Automatic machines frequently comprise a cutting unit for cutting a continuous, reel-fed strip into individually used portions.
One example of a cutting unit employed on an automatic machine is described in Patent EP-0654329-B1, which describes a cutting unit for cutting a conveyor-fed strip into portions. The cutting unit comprises a number of inner blades with respective cutting edges parallel to one surface of the strip, and corresponding outer blades with respective cutting edges sloping with respect to those of the inner blades. Each inner blade moves with the conveyor through the cutting station in time with the corresponding outer blade, is gradually moved through the conveyor into a cutting position, and is gradually engaged by the sloping cutting edge of the corresponding outer blade to scissor-cut the strip.
Another example of a cutting unit employed on an automatic machine is described in U.S. Pat. No. 4,943,341-A1, which describes a cutting unit for cutting bands successively off a strip by means of two cutting drums fitted with a number of blades; each blade on one drum defines, with a blade on the other drum, a pair of scissors for cutting the strip at successive points as the drums rotate.
Another example of a cutting unit employed on an automatic machine is described in U.S. Pat. No. 4,943,341-A1, which describes a cutting unit for cutting filter-cigarette bands on a high-speed filter assembly machine; the bands are cut successively off a strip by two counter-rotating cutting drums, each fitted with a number of equally spaced blades; and each blade on one drum defines, with a blade on the other drum, scissor means by which to cut the strip at successive points as the drums rotate.
During normal operation of a cutting unit of the type described above, mutual contact of the blades tends to wear them down and so eventually impair efficiency, which results in a gradual increase in the number of rejects and in jamming of the machine caused by cutting problems. For this reason, an operator adjusts the cutting unit at predetermined intervals, and, after another predetermined interval or predetermined number of adjustments, the cutting unit is dismantled for overall servicing.
Using the above maintenance method, however, the number of rejects and the extent to which the machine is subject to jamming caused by cutting problems still remain, on average, serious considerations, or the working life of the cutting unit is particularly short, depending on the length of the set adjustment intervals. Determining the best length of set adjustment intervals has always proved complicated on account of dispersion and drift in the construction and operating characteristics of different cutting units. Moreover, the best length is seriously affected by the characteristics of the strip being cut, and is therefore substantially impossible to determine when the type of strip used on the automatic machine is changed frequently.